The commercial preparation of hydroxyl-terminated liquid polymers having an aliphatic polymeric backbone and sulfide likages near the terminal portions of the polymer molecule has increased steadily over the past few years. The successful preparation of these liquid polymers (hereinafter referred to as "HTPS polymers" for brevity), depends upon the selection of chain terminator, and the amount of chain terminator used.
The preparation of HTPS polymers is described in U.S. Pat. Nos. 3,910,992; 4,013,710; and 4,120,766 ("the '766 patent"); the disclosures of each of which is incorporated by reference herein as if fully set forth. In particular, the '766 patent discloses the reaction of at least one vinylidene monomer with at least one hydroxyl-containing disulfide, which reaction provides particularly desirable HTPS polymers believed to have the formula EQU OH--X--(S)--(D)--(S)--X--OH
wherein, X is (CH.sub.2 O).sub.m (CH.sub.2).sub.n or ##STR1##
m is an integer from 0 to 10; and n is an integer from 1 to 10, and, D is an aliphatic backbone containing polymerized units of the vinylidene monomer. Excellent results were obtained when m was 0 and n was 2.
The hydroxyl containing disulfide has the formula EQU HO(CH.sub.2 O).sub.m (CH.sub.2).sub.n --S--S--(CH.sub.2).sub.n (OCH.sub.2).sub.m OH or ##STR2## wherein, m and n have the same connotation as hereinabove.
The preparation of dithiodialkylene glycols is described in U.S. Pat. Nos. 2,746,994 and 2,754,333; and of polythiodiglycols in U.S. Pat. No. 3,778,478 ("the '478 patent"). In the process of the '478 patent, when diethanol disulfide (hereafter referred to as "DEDS" for brevity) is desired, it is formed in a first reaction by adding the stoichiometrically required amount of sulfur, to ethylene oxide dissolved in a solvent through which H.sub.2 S is bubbled. DEDS is also named 2,2'-dithiodiethanol, or bis(2-hydroxyethyl) disulfide, or 2,2'-dihydroxydiethyl disulfide, or diethanol disulfide, or dithiodiglycol, or diethylene glycol disulfide, and less correctly, 2-hydroxyethyl disulfide. Though the DEDS is predominantly formed as expected, there is also formed an unpredictable amount of diethanol trisulfide (hereafter referred to as "DETS" for brevity). Thus the mixture has an unpredictable ratio of the di- and trisulfides.
Thereafter, an analogous second reaction is repeated with the stoichiometric amount of sulfur required to form the DETS. Though the trisulfide is predominantly formed as expected, there is also formed an unpredictable amount of di-and tetrasulfides. The content of the di- and tetrasulfides in the second reaction is determined; if the tetrasulfide content is not high enough to be a problem, the reaction products of the first and second reactions are mixed in the proportions required to yield a predetermined ratio of di- and tri-sulfides. Though the foregoing procedure does yield any preselected ratio of di- and tri-sulfides, it is time-consuming and relatively more costly than the two-step process of my invention which process requires no analysis of reaction products, because the process yields only a mixture of di- and tri-sulfides in the preselected ratio.
Other preparations for polysulfides are disclosed in a chapter on "Organic Sulfur Compounds", in ORGANIC CHEMISTRY, Vol. I, 2d edition by Gilman, J. Wiley & Sons, New York; and in an article titled ".beta..beta.'-dichlorodiethyl disulfide" in J. Chem. Soc., 119, 418 (1921), by Bennet, G. M.
During the investigation of sulphur vesicants, reported in an article titled "New Organic Vesicants. Part IV. 1:2-Di-(2-chloroethylthio)ethane and its Analogues" by Gasson, E. J. Williams, A. H. and Woodward F. N., J. Chem. Soc. (London), 44 (1948), 2-hydroxyethanethiol was oxidized by the careful addition of 30.5% w/v hydrogen peroxide, the temperature being kept below 50.degree.. After removal of the water under low pressure, a thick colorless syrup remained which could not be induced to crystallise, but could be distilled in small batches, if done quickly. The pure dihydroxy-disulfide (DEDS) was obtained as an intermediate which was then converted to the chloro-compound by means of thionyl chloride.